U.S. patent application number 14/144385 was filed with the patent office on 2014-09-11 for method of fabricating polyene containing polarizing film, polyene containing polarizing film fabricated using the same, polarizing plate including the same, and display including the same.
This patent application is currently assigned to Cheil Industries Inc.. The applicant listed for this patent is Chell Industries Inc.. Invention is credited to Shigeto Kobori, Atsushi Sato, Takashi Takagi.
Application Number | 20140255678 14/144385 |
Document ID | / |
Family ID | 51488162 |
Filed Date | 2014-09-11 |
United States Patent
Application |
20140255678 |
Kind Code |
A1 |
Kobori; Shigeto ; et
al. |
September 11, 2014 |
METHOD OF FABRICATING POLYENE CONTAINING POLARIZING FILM, POLYENE
CONTAINING POLARIZING FILM FABRICATED USING THE SAME, POLARIZING
PLATE INCLUDING THE SAME, AND DISPLAY INCLUDING THE SAME
Abstract
A method of fabricating a polarizing film having excellent
optical properties. The method includes fabricating a polyvinyl
alcohol film using a coating liquid including an acid catalyst and
a polyvinyl alcohol, and dehydrating the polyvinyl alcohol film. In
this method, a high concentration of the acid catalyst is uniformly
dispersed in the polyvinyl alcohol film.
Inventors: |
Kobori; Shigeto;
(Yokohamashi, JP) ; Takagi; Takashi; (Yokohamashi,
JP) ; Sato; Atsushi; (Yokohamashi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Chell Industries Inc. |
Gumi-si |
|
KR |
|
|
Assignee: |
Cheil Industries Inc.
Gumi-si
KR
|
Family ID: |
51488162 |
Appl. No.: |
14/144385 |
Filed: |
December 30, 2013 |
Current U.S.
Class: |
428/220 ;
264/1.34; 427/163.1; 524/557 |
Current CPC
Class: |
G02B 5/305 20130101;
G02B 1/08 20130101 |
Class at
Publication: |
428/220 ;
524/557; 427/163.1; 264/1.34 |
International
Class: |
H01L 51/52 20060101
H01L051/52; G02B 1/04 20060101 G02B001/04; H01L 51/56 20060101
H01L051/56; G02B 1/08 20060101 G02B001/08 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2012 |
JP |
2012-287727 |
Sep 25, 2013 |
KR |
10-2013-0114116 |
Claims
1. A method of fabricating a polyene containing polarizing film,
comprising: fabricating a polyvinyl alcohol film using a coating
liquid comprising an acid catalyst and a polyvinyl alcohol; and
dehydrating the polyvinyl alcohol film.
2. The method according to claim 1, wherein the acid catalyst is an
acid with low volatility.
3. The method according to claim 2, wherein the acid catalyst has a
weight loss rate of less than about 3 wt % at 100.degree. C.
4. The method according to claim 2, wherein the acid catalyst
comprises an organic acid.
5. The method according to claim 4, wherein the organic acid
comprises a functional group selected from the group consisting of
a carboxylic acid group and a sulfonic acid group.
6. The method according to claim 1, wherein the coating liquid
comprises the acid catalyst in an amount of about 2 wt % to about
10 wt % based on a weight of the polyvinyl alcohol.
7. The method according to claim 6, wherein the coating liquid
comprises the acid catalyst in an amount of about 4.0 wt % to about
10.0 wt % based on the weight of the polyvinyl alcohol.
8. The method according to claim 7, wherein the coating liquid
comprises the acid catalyst in an amount of 5 wt % based on the
weight of the polyvinyl alcohol.
9. The method according to claim 1, wherein the polyvinyl alcohol
has a degree of polymerization from about 1500 to about 5000.
10. The method according to claim 1, further comprising: wet
stretching the polyvinyl alcohol film after dehydration.
11. The method according to claim 10, wherein the wet stretching
comprises stretching the polyvinyl alcohol film in an aqueous
solution of boric acid at a temperature of about 20.degree. C. to
60.degree. C.
12. A polyene containing polarizing film fabricated by the method
according to claim 1.
13. The polyene containing polarizing film according to claim 12,
wherein the polyene containing polarizing film has a thickness of
less than about 10 .mu.m.
14. A polyene containing polarizing film fabricated from a
polyvinyl alcohol film comprising an acid catalyst.
15. A polarizing plate comprising the polyene containing polarizing
film according to claim 12.
16. The polarizing plate according to claim 15, wherein the
polarizing plate has a transmittance of about 44% or more and a
degree of polarization of about 97% or more.
17. A display comprising a polarizing plate according to claim 15.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to and the benefit of
Japanese Patent Application No. 2012-287727, filed in the Japanese
Patent Office on Dec. 28, 2012, and Korean Patent Application No.
10-2013-0114116, filed in the Korean Intellectual Property Office
on Sep. 25, 2013, the entire contents of both are incorporated
herein by reference.
BACKGROUND
[0002] 1. Field
[0003] The following description relates to a method of fabricating
a polyene containing polarizing film, a polyene containing
polarizing film, a polarizing plate, and a display.
[0004] 2. Description of the Related Art
[0005] In organic light emitting displays using organic light
emitting diodes (OLED), a polarizing film is required to have
improved transmittance. Iodine based polarizing films are known and
broadly used as polarizing films for various displays.
[0006] In the iodine based polarizing film, a main component for
the polarization function (namely, the component that absorbs
visible light) is iodine. Thus, it is necessary to decrease the
amount of iodine in the polarizing film in order to increase the
transmittance of the polarizing film. However, since iodine may be
sublimated under high temperature and high humidity conditions, the
polarizing film may suffer from a lack of iodine if the amount of
iodine in the polarizing film is decreased, thereby causing
significant reduction in the degree of polarization of the
polarizing film. As a result, the iodine based polarizing film
having high transmittance (for example, transmittance of 44% or
more) suffers from a reduction in long term reliability under high
temperature and high humidity conditions.
[0007] To resolve such a problem, a dye-based polarizing film and a
polyene containing polarizing film disclosed in JP2006-99076 A are
known in the art. The dye-based polarizing film may exhibit
excellent heat resistance even when the dye-based polarizing film
has high transmittance. However, the dye-based polarizing film has
a drawback in that the degree of polarization is likely to decrease
when the dye-based polarizing film has high transmittance.
[0008] Although the polyene containing polarizing film has a
slightly lower degree of polarization than the iodine based
polarizing film, the polyene containing polarizing film has an
advantage in that, even when the polyene containing polarizing film
exhibits high transmittance, the polyene containing polarizing film
still has high reliability under high temperature and high humidity
conditions. This is because the main component for polarization
(namely, the component that absorbs visible light) in the polyene
containing polarizing film is polyene (specifically, the
carbon-carbon double bonds). The carbon-carbon double bonds are not
affected by temperature or humidity. Thus, the polyene containing
polarizing film exhibits (basically exhibits) high durability under
high temperature and high humidity conditions. For this reason, the
polyene containing polarizing film has attracted considerable
attention as a polarizing film for displays.
[0009] As a method of fabricating a polyene containing polarizing
film, a process of dehydrating polyvinyl alcohol (PVA) using an
acid catalyst is known in the art. Specifically, a polyvinyl
alcohol film is impregnated in an aqueous solution of an acid
catalyst, followed by heat treatment of the polyvinyl alcohol film
to dehydrate polyvinyl alcohol, thereby fabricating a polyene
containing polarizing film. As the acid catalyst, hydrochloric acid
or sulfuric acid is used.
[0010] However, when hydrochloric acid is used as the acid
catalyst, the acid catalyst is evaporated as hydrogen chloride gas
together with the evaporation of water upon heat treatment of the
polyvinyl alcohol film. As a result, it becomes very difficult to
control the acid concentration in the polyvinyl alcohol film. When
there is deviation in the acid concentration of polyvinyl alcohol,
the polyene containing polarizing film is likely to suffer from
deviation or non-uniformity in the optical properties, such as
transmittance, degree of polarization, or the like.
[0011] In order to solve these problems, it is contemplated that
the acid concentration in the polyvinyl alcohol film may be made
uniform by controlling temperature, humidity and atmosphere during
heat treatment. However, this method requires a complicated
structure of a fabrication apparatus.
[0012] On the other hand, sulfuric acid is not easily evaporated
(volatilized). However, since sulfuric acid had an excessively
strong dehydration function, sulfuric acid may provide undesirable
effects, such as dehydration between molecules upon heat treatment
or PVA backbone breakage, and may easily deteriorate the optical
properties of the polyene containing polarizing film, when used as
the acid catalyst.
[0013] As such, a typical method of fabricating a polyene
containing polarizing film does not satisfy the requirement of
production stability and optical performance. Japanese Patent
Publication No. 2006-099076A discloses the use of an organic acid
as the acid catalyst. However, even in this case, it is difficult
to obtain constant acid concentration in polyvinyl alcohol.
[0014] Therefore, one or more embodiments of the present invention
are directed toward a method of fabricating an improved polarizing
film capable of stably preparing a polarizing film having excellent
optical properties.
SUMMARY
[0015] According to an embodiment of the present invention, a
method of fabricating a polyene containing polarizing film
includes: fabricating a polyvinyl alcohol film using a coating
liquid including an acid catalyst and polyvinyl alcohol, and
dehydrating the polyvinyl alcohol film. According to this
embodiment, since it is possible to uniformly disperse the acid
catalyst at high concentration in the polyvinyl alcohol film, a
polyene containing polarizing film having multiple carbon-carbon
double bonds uniformly formed therein may be fabricated without the
need of accurate control of the environmental conditions such as
temperature or the like as in the related art. Therefore, according
to this embodiment, it is possible to achieve fabrication of a
stable polarizing film having both high degree of polarization and
high transmittance, namely, excellent optical properties.
[0016] Here, the acid catalyst may be a low volatility acid
catalyst. According to this embodiment, the acid catalyst has low
volatility and thus is unlikely to evaporate in the preparation of
polyene. Thus, the method according to this embodiment may provide
a more uniform acid concentration in the polyvinyl alcohol film in
preparation of polyene.
[0017] In addition, the acid catalyst may have a weight loss rate
of less than about 3 wt % at 100.degree. C. According to this
embodiment, since the acid catalyst has a weight loss rate of less
than about 3 wt % at 100.degree. C., the acid catalyst is unlikely
to evaporate in preparation of polyene. Thus, the method according
to this embodiment may provide a more uniform acid concentration in
the polyvinyl alcohol in preparation of polyene.
[0018] Further, the acid catalyst may be an organic acid. According
to this embodiment, since the acid catalyst is an organic acid, the
acid catalyst is unlikely to evaporate in preparation of polyene.
Thus, the method according to this embodiment may provide a more
uniform acid concentration in the polyvinyl alcohol in preparation
of polyene.
[0019] Further, the organic acid may have a functional group
selected from the group consisting of a carboxylic acid group and a
sulfonic acid group. According to this embodiment, since the
organic acid has a functional group selected from the group
consisting of a carboxylic acid group and a sulfonic acid group,
the acid catalyst is unlikely to evaporate in preparation of
polyene. Thus, the method according to this embodiment may provide
a more uniform acid concentration in the polyvinyl alcohol in
preparation of polyene.
[0020] Further, the coating liquid may include the acid catalyst in
an amount of about 2 wt % to about 10 wt % based on the weight of
the polyvinyl alcohol. According to this embodiment, the coating
liquid includes the acid catalyst in an amount of about 2 wt % to
about 10 wt % based on the weight of the polyvinyl alcohol.
Accordingly, the method according to this embodiment may fabricate
a polyene containing polarizing film having high degree of
polarization as well as high transmittance.
[0021] Further, the coating liquid may include the acid catalyst in
an amount of about 4.0 wt % to about 10.0 wt % based on the weight
of the polyvinyl alcohol. According to this embodiment, the coating
liquid includes the acid catalyst in an amount of about 4.0 wt % to
about 10.0 wt % based on the weight of the polyvinyl alcohol.
Accordingly, the method according to this embodiment may fabricate
a polyene containing polarizing film having high degree of
polarization as well as high transmittance.
[0022] Further, the content (or amount) of acid catalyst may be
about 5 wt % based on the weight of the polyvinyl alcohol.
According to this embodiment, since the content of the acid
catalyst is about 5 wt % based on the weight of the polyvinyl
alcohol, the method according to this embodiment may fabricate a
polyene containing polarizing film having high degree of
polarization as well as high transmittance.
[0023] According to another embodiment of the present invention, a
polyene containing polarizing film may be fabricated by the method
according to embodiments of the present invention. Since the
polyene containing polarizing film according to this embodiment of
the invention has both high degree of polarization and high
transmittance, the polyene containing polarizing film is suitable
for, for example, organic light emitting displays.
[0024] Here, the polyene containing polarizing film may have a
thickness of less than about 10 .mu.m. According to this
embodiment, since the polyene containing polarizing film has a
thickness of less than about 10 .mu.m, shrinkage of the polyene
containing polarizing film may be reduced even when the polyene
containing polarizing film is applied to a large organic light
emitting display. As a result, according to this embodiment,
warpage or curling of the organic light emitting display may be
reduced.
[0025] According to a further embodiment of the present invention,
a polarizing plate may include the polyene containing polarizing
film manufactured according to embodiments of the present
invention. According to this embodiment of the present invention,
since the polarizing plate has both high degree of polarization and
high transmittance, the polarizing plate is suitable for, for
example, organic light emitting displays.
[0026] According to yet another embodiment of the present
invention, a display may include the polarizing plate manufactured
according to embodiments of the present invention. According to
this embodiment of the present invention, since the display
includes the polarizing plate having both high degree of
polarization and high transmittance, the display has excellent
optical properties.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1(a) is a sectional view of a polarizing film in the
related art; and
[0028] FIG. 1(b) is a sectional view of a polarizing film according
to one embodiment of the present invention.
DETAILED DESCRIPTION
[0029] Embodiments will now be described in more detail with
reference to the accompanying drawing. In the specification and
drawings, components having substantially the same functions will
be represented by the same reference numerals, and repeated
descriptions thereof will be omitted.
[0030] Method of Fabricating a Polarizing Film
[0031] First, a method of fabricating a polarizing film according
to one embodiment of the present invention will be described. The
polyene containing polarizing film according to one embodiment of
the invention is fabricated from a polyvinyl alcohol film including
an acid catalyst. The method according to one embodiment of the
present invention includes fabricating a polyvinyl alcohol film
using a coating liquid including an acid catalyst and polyvinyl
alcohol, and dehydrating the polyvinyl alcohol film.
[0032] Fabrication of a Polyvinyl Alcohol Film
[0033] In fabricating a polyvinyl alcohol film, a coating liquid
including an acid catalyst and polyvinyl alcohol is prepared. Here,
polyvinyl alcohol is introduced into water, followed by stirring
and heating the mixture of water and polyvinyl alcohol, thereby
sufficiently dissolving polyvinyl alcohol in water. Subsequently,
an acid catalyst and a leveling agent are introduced into the
aqueous solution of polyvinyl alcohol, followed by stirring to
prepare a coating liquid.
[0034] Polyvinyl alcohol may have a degree of polymerization from
about 1500 to about 5000, for example, from about 1500 to about
2500. For example, polyvinyl alcohol may have a degree of
polymerization of about 1500, 1600, 1700, 1800, 1900, 2000, 2100,
2200, 2300, 2400 or 2500. Within this range, it is possible to
reduce or prevent breakage of the polyvinyl alcohol film even upon
wet stretching.
[0035] Polyvinyl alcohol may have a degree of saponification from
about 95 mol % to about 100 mol %, for example, about 99.9 mol %.
Within this range, the polyvinyl alcohol film may exhibit excellent
durability and high stretchability.
[0036] In this embodiment, the acid catalyst may be pre-mixed with
the coating liquid. As a result, polyvinyl alcohol may have a
uniform acid concentration. Namely, the acid catalyst may be more
uniformly dispersed in polyvinyl alcohol.
[0037] The acid catalyst may be a low volatility acid catalyst,
without being limited thereto. When the acid catalyst has low
volatility, evaporation of the acid catalyst may be reduced or
prevented in preparation of polyene, thereby providing a more
stable (and uniform) acid concentration in polyvinyl alcohol.
[0038] In one embodiment, the acid catalyst may have a weight loss
of less than about 3 wt % at 100.degree. C. When the weight loss
rate of the acid catalyst at 100.degree. C. is less than about 3 wt
%, for example, from about 0.1 wt % to about 2.5 wt %, the acid
concentration in polyvinyl alcohol may become more stable and more
uniform in preparation of polyene. For example, the weight loss
rate of the acid catalyst at 100.degree. C. may be about 0.1 wt %,
0.2 wt %, 0.3 wt %, 0.4 wt %, 0.5 wt %, 0.6 wt %, 0.7 wt %, 0.8 wt
%, 0.9 wt %, 1.0 wt %, 1.1 wt %, 1.2 wt %, 1.3 wt %, 1.4 wt %, 1.5
wt %, 1.6 wt %, 1.7 wt %, 1.8 wt %, 1.9 wt %, 2.0 wt %, 2.1 wt %,
2.2 wt %, 2.3 wt %, 2.4 wt %, 2.5 wt %, 2.6 wt %, 2.7 wt %, 2.8 wt
%, or 2.9 wt %. The weight loss rate refers to a percentage
obtained by measuring the initial weight of the acid catalyst and
the weight of the acid catalyst after heating at 100.degree. C. for
10 minutes, and dividing an absolute difference therebetween by the
initial weight.
[0039] For example, the acid catalyst satisfying the aforementioned
requirements may be an organic acid. The organic acid may have a
functional group selected from the group consisting of carboxylic
acid group and a sulfonic acid group, but is not limited thereto.
The organic acid may be represented by R--X. Here, R may be any
compound formed of carbon, hydrogen and fluorine, without
limitation. For example, R may be a functional group selected from
the group consisting of a C.sub.1 to C.sub.12 alkyl group, a
C.sub.1 to C.sub.12 perfluoroalkyl group, a C.sub.6 to C.sub.12
aromatic functional group, and a C.sub.6 to C.sub.12 fluorine
substituted aromatic functional group. X is a functional group
selected from the group consisting of a carboxylic acid group and a
sulfonic acid group. For example, the organic acid may be
paratoluene sulfonic acid.
[0040] For example, the weight loss rate of paratoluene sulfonic
acid upon heating at 100.degree. C. for 10 minutes is below a
detection limit (10 ppm or less) of an analytical instrument. The
analytical instrument may include ion chromatography, or the like.
The analysis includes heating a sample on a hot plate to collect
the resulting gases. Subsequently, the gases are subjected to
bubbling in water to substitute the gases. Then, quantitative
analysis is performed through ion chromatography.
[0041] Further, since the concentration of a saturated aqueous
solution of paratoluene sulfonic acid is higher than that of
hydrochloric acid, an acid catalyst having a higher concentration
may be dispersed in polyvinyl alcohol if paratoluene sulfonic acid
is used as the acid catalyst. In addition, although the acid
catalyst remaining in the polyene containing polarizing film may
reduce durability of the polyene containing polarizing film, the
paratoluene sulfonic acid may be more easily removed from the
polyene containing polarizing film than hydrochloric acid.
[0042] Although the content ratio of the acid catalyst is not
particularly limited, the acid catalyst may present in an amount of
2 wt % to 10 wt %, for example, 4.0 wt % to 10.0 wt %, based on the
weight of polyvinyl alcohol. Within this range, reaction time may
be reduced while inhibiting side reaction. For example, the acid
catalyst may present in an amount of about 2 wt %, 2.5 wt %, 3.0 wt
%, 3.5 wt %, 4.0 wt %, 4.5 wt %, 5.0 wt %, 5.5 wt %, 6.0 wt %, 6.5
wt %, 7.0 wt %, 7.5 wt %, 8.0 wt %, 8.5 wt %, 9.0 wt %, 9.5 wt %,
or 10 wt % based on the weight of polyvinyl alcohol.
[0043] Further, dehydration may be easily controlled while
preventing corrosion of the fabrication apparatus. For example,
when the content of the acid catalyst is less than 4 wt % based on
the weight of polyvinyl alcohol, it takes more than 10 minutes to
initiate dehydration reaction at a dehydration temperature of
140.degree. C. and it takes a long time to complete the dehydration
reaction (provided that the dehydration reaction proceeds).
[0044] In one embodiment, the acid catalyst may present in an
amount of about 5 wt % based on the weight of polyvinyl alcohol. In
this content of the acid catalyst, a polyene containing polarizing
film having both high transmittance and high degree of polarization
may be fabricated. The degree of polarization of the polyene
containing polarizing film may be controlled by the content of the
acid catalyst. A higher amount of the acid catalyst provides a
higher amount of polyene (namely, carbon-carbon double bonds) in
polyvinyl alcohol, thereby increasing the degree of
polarization.
[0045] Transmittance tends to increase as the distribution of
components contributing to polarization (such as the carbon-carbon
double bonds in a polyene containing polarizing film, iodine in an
iodine based polarizing film, or the like) becomes uniform. Since a
typical method of fabricating a polyene containing polarizing film
fails to achieve a uniform acid concentration in polyvinyl alcohol,
the polyene containing polarizing film has a non-uniform
distribution of carbon-carbon double bonds. For this reason, the
polarizing film has a non-uniform degree of polarization and
non-uniform transmittance. Conversely, according to the embodiment
of the present invention, since the acid catalyst is previously
added to polyvinyl alcohol (i.e., the acid catalyst is added to
polyvinyl alcohol to make a coating liquid before forming the
polyvinyl alcohol film), a desired concentration of the acid
catalyst may be more uniformly dispersed in polyvinyl alcohol.
Therefore, in the method according to the embodiment of the present
invention, it is possible to fabricate a polyene containing
polarizing film having both high transmittance and high degree of
polarization.
[0046] The leveling agent may be a perfluoroalkylethylene oxide
adduct, without being limited thereto.
[0047] Next, the coating liquid is coated onto a substrate (for
example, a non-stretched film), followed by drying the coating
liquid to form a polyvinyl alcohol film on the substrate. Although
the thickness of the polyvinyl alcohol film is not particularly
limited, the thickness of the polyvinyl alcohol film may be
adjusted to about 10 .mu.m or less. In one embodiment, the
polyvinyl alcohol film including the acid catalyst may have a
thickness of about 0.5 .mu.m to about 10.0 .mu.m. Within this
range, the polyvinyl alcohol film may be used for polarizing
plates, and may be reduced or prevented from breaking upon
elongation.
[0048] Dehydration of Polyvinyl Alcohol
[0049] In dehydrating polyvinyl alcohol, polyvinyl alcohol in the
polyvinyl alcohol film is subjected to dehydration to form polyene
(carbon-carbon double bonds). Here, the polyvinyl alcohol film is
heated to perform dehydration of polyvinyl alcohol. In this
embodiment, since the acid catalyst is uniformly dispersed in
polyvinyl alcohol film, carbon-carbon double bonds are uniformly
generated in polyvinyl alcohol film. Temperature and time for
heating are not particularly limited and may be suitably adjusted
according to a desired degree of polarization.
[0050] While performing dehydration of polyvinyl alcohol, the
polyvinyl alcohol film may be stretched in a set or predetermined
direction. Hereinafter, stretching performed in a liquid will be
referred to as "wet stretching", while stretching performed in a
gas (for example, in an atmosphere) will be referred to as "dry
stretching". By such stretching operation, orientations of the
carbon-carbon double bonds may be coincided with each other.
Further, the polyvinyl alcohol film may be stretched in a ratio
from about 1.1 to about 6 times an initial length thereof, for
example, about 4 times, or for example, about 1.5, 2.0, 2.5, 3.0,
3.5, 4.0, 4.5, 5.0, 5.5, or 6 times, without being limited thereto.
Dry stretching and wet stretching described below may be performed
after aligning the film with the substrate.
[0051] Dehydration and dry stretching may include treating the
polyvinyl alcohol film at about 50.degree. C. to about 150.degree.
C. for about 1 minute to 20 minutes.
[0052] Next, the polyvinyl alcohol film is dipped in an aqueous
solution of boric acid, followed by stretching the film in the
aqueous solution of boric acid in the same direction as in dry
stretching. Namely, polyvinyl alcohol is wet stretched. Wet
stretching may be performed to have a stretch ratio ranging from
about 1.1 times to 3.5 times, for example about 1.5 times of the
length before conducting the wet stretching, without being limited
thereto. When the stretch ratio of dry stretching is 4 times and
the stretch ratio of wet stretching is 1.5 times, the polyvinyl
alcohol film is stretched in a total of 6 times the initial length
thereof. Subsequently, the polyvinyl alcohol film is dried to form
a polyene containing polarizing film. The aqueous solution of boric
acid may be an aqueous solution containing about 0.1 wt % to about
5 wt % of boric acid. Within this range, the polyene may have the
effect of securing the double bonds.
[0053] Wet stretching may include the act of stretching the
polyvinyl alcohol film in an aqueous solution of boric acid at
about 20.degree. C. to about 60.degree. C. (for example, at about
20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36,
37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53,
54, 55, 56, 57, 58, 59, or 60.degree. C.) for about 1 minute to
about 20 minutes.
[0054] As such, according to this embodiment, since the acid
catalyst is added to the coating liquid, it is possible to
uniformly disperse the acid catalyst of high concentration in the
polyvinyl alcohol film. Accordingly, according to this embodiment,
it is possible to fabricate a polyene containing polarizing film in
which multiple carbon-carbon double bonds are uniformly dispersed.
Namely, in this embodiment, it is possible to fabricate a polyene
containing polarizing film having both high degree of polarization
and high transmittance. Further, in this embodiment, non-uniformity
of the polyene containing polarizing film may be decreased.
Further, since impregnation of polyvinyl alcohol in an aqueous
solution of the acid catalyst becomes unnecessary, the fabrication
process may be simplified.
[0055] In this embodiment, since the acid catalyst is added to the
coating liquid, the acid catalyst of high concentration may be
uniformly dispersed in the polyvinyl alcohol film even if a
polyvinyl alcohol film is formed to a low thickness. Accordingly,
in this embodiment, the polyene containing polarizing film having a
low thickness, a high degree of polarization, and high
transmittance may be fabricated. For example, in this embodiment,
the polyene containing polarizing film may have a thickness of less
than about 10 .mu.m, for example, from about 1 .mu.m to about 5
.mu.m, a transmittance of about 44% or more, for example, from
about 44% to about 46%, and a degree of polarization of about 97%
or more, for example, from 98% to 100%. When the organic acid is
used as the acid catalyst, evaporation of the acid catalyst in
preparation of polyene may be reduced or inhibited, thereby
enhancing the degree of polarization.
[0056] On the other hand, in a comparable method in the related
art, the polyvinyl alcohol film is impregnated in the aqueous
solution of an acid catalyst such as hydrochloric acid. However,
when the polyvinyl alcohol film has a thin thickness, it is
difficult to impregnate the polyvinyl alcohol film with a
sufficient amount of the acid catalyst. Further, since hydrochloric
acid is likely to volatilize, hydrochloric acid may be evaporated
in preparation of polyene. For this reason, in the comparable
method, polyene, that is, the carbon-carbon double bonds are
insufficiently produced, thereby making it difficult to fabricate a
polyene containing polarizing film which has a thin thickness and
exhibits a high degree of polarization.
[0057] The acid catalyst may be removed by dipping the polyene
containing polarizing film in water or in an aqueous inorganic
solution, such as a weak alkali water solution, a saline solution,
or the like.
[0058] The acid catalyst may present in an amount of about 0.001 wt
% or less in the polyene containing polarizing film. Within this
range, the acid catalyst may not influence the properties of the
polarizing film, such as the degree of polarization, transmittance,
or the like.
[0059] The polyene containing polarizing film is then separated
from the substrate and is combined with a protective film and a
retardation film (.lamda./4 film), and the like to fabricate a
polarizing plate.
[0060] One example of the polarizing plate is shown in FIGS. 1(a)
and 1(b). FIG. 1(b) shows a polarizing plate 10 according to one
embodiment of the invention compared with a typical iodine based
polarizing plate 100 shown in FIG. 1(a). Here, FIG. 1(a) shows a
typical iodine based polarizing plate 100 and FIG. 1(b) shows a
polarizing plate 10 according to one embodiment of the
invention.
[0061] A typical polarizing plate 100 includes an iodine based
polarizing film 110, protective films 120 and 130, pressure
sensitive adhesive layers 140 and 160, and a retardation film
(.lamda./4 film) 150. The iodine based polarizing film 110 has a
high thickness to achieve a desired degree of polarization. For
example, the iodine based polarizing film 110 may have a thickness
of 22 .mu.m or more. As a result, the overall thickness of the
polarizing plate 100 increases. For example, the polarizing plate
100 may have a thickness of 190 .mu.m or more.
[0062] The polarizing plate 10 according to one embodiment may
include a polyene containing polarizing film 11, UV adhesive layers
12 and 14, a protective film 13, a retardation film (.lamda./4
film) 15, and a pressure sensitive adhesive layer 16.
[0063] Accordingly, the polarizing plate 10 is made of a circularly
polarizing film. Further, the polarizing plate 10 according to this
embodiment may be made of suitable known materials in addition to
the polyene containing polarizing film 11. The pressure sensitive
adhesive layer 16 is adhered to, for example, a display side of a
display device. In this embodiment, since the polyene containing
polarizing plate 11 has a low thickness, the overall polarizing
plate 10 including the polyene containing polarizing film also has
a low thickness. In this embodiment, the polarizing plate 10 may
have a thickness of 100 .mu.m or less. It should be understood that
the polarizing plate according to the present invention may have
different structures. The polarizing plate may not be a circularly
polarizing film. The polarizing plate may have a transmittance of
about 44% or more, for example, from about 44% to about 46%, and a
degree of polarization of about 97% or more, for example, from
about 98% to about 100%.
EXAMPLE
Example 1
[0064] One embodiment of the present invention is described in
Example 1. In Example 1, a polyene containing polarizing film and a
polarizing plate were fabricated as follows.
[0065] Fabrication of a Polyvinyl Alcohol Film
[0066] First, polyvinyl alcohol (JC-25, Japan VAM & POVAL Co.,
Ltd.) was introduced into water as a solvent. The mixture of water
and polyvinyl alcohol was heated while being stirred, thereby
sufficiently dissolving polyvinyl alcohol in water. Paratoluene
sulfonic acid and a leveling agent (Megapak, DIC Corporation) were
added to the aqueous solution of polyvinyl alcohol, followed by
stirring to prepare a coating liquid. The impregnation ratio
(weight ratio) of water, polyvinyl alcohol and paratoluene sulfonic
acid in the coating liquid was 89.5 wt %:10 wt %:0.5 wt %. Further,
the content of the leveling agent was a minor amount. That is, the
leveling agent was present in an amount of 0.002 wt % based on the
total weight of water, polyvinyl alcohol and paratoluene sulfonic
acid.
[0067] Next, a non-stretched film formed of isophthalic acid
copolymeric polyethylene terephthalate (PET) was prepared as a
substrate, followed by coating the coating liquid onto the
substrate. Subsequently, the coating liquid was dried to fabricate
a polyvinyl alcohol film. The polyvinyl alcohol film had a
thickness of 10 .mu.m.
[0068] Dehydration of Polyvinyl Alcohol
[0069] The polyvinyl alcohol film was placed in an oven preheated
to 140.degree. C., followed by heating at 140.degree. C. for 120
seconds, thereby dehydrating polyvinyl alcohol from the polyvinyl
alcohol film to prepare polyene (carbon-carbon double bonds). While
performing dehydration of the polyvinyl alcohol, the polyvinyl
alcohol film and the substrate were aligned and dry stretched to 4
times the initial length thereof in a set or predetermined
direction.
[0070] Next, the polyvinyl alcohol film was dipped into an aqueous
solution of 5 wt % boric acid (containing 5 wt % boric acid based
on the total weight of the aqueous solution) preheated to
85.degree. C. The polyvinyl alcohol film and the substrate were
subjected to wet stretching to 1.5 times the initial length thereof
(i.e., the length of the polyvinyl alcohol film prior to the wet
stretching) in the aqueous solution of boric acid in the same
direction as the dry stretching. As a result, the polyvinyl alcohol
film was stretched to a total length of 6 times the initial length
thereof. Thereafter, the polyvinyl alcohol film was placed in an
oven preheated to 80.degree. C., followed by drying at 80.degree.
C. for 2 minutes, thereby fabricating a polyene containing
polarizing film prepared in Example 1. The polyene containing
polarizing film had a thickness of 5 .mu.m.
[0071] Subsequently, a UV adhesive was prepared using the following
components.
[0072] 90 wt % of (a), 10 wt % of (b), 1 wt % of (c) and 2 wt % of
(d) were mixed using a stirrer. The content ratio of (c) and (d)
was respectively calculated based on the total weight of
(a)+(b).
[0073] (a) 4HBA (4-hydroxybutyl acrylate)
[0074] (b) Celloxide 2021P (3,4-epoxycyclohexylmethyl
3,4-epoxycyclohexane carboxylate) (Daicel Corporation)
[0075] (c) TPO (2,4,6-trimethylbenzoyl-diphenyl-phospine oxide)
(Ciba Specialty Chemicals Holding Inc.)
[0076] (d) CPI-110P ((p-phenylthiophenyl)diphenyl sulfonium
PF.sub.6.sup.- salt) (SAN-APRO LTD.)
[0077] The UV adhesive was applied to a thickness of 2 .mu.m on a
surface of the polyene containing polarizing film (a surface
opposite to the one contacting the substrate). Subsequently, a 50
.mu.m thick protective film (UV absorber-containing triacetyl
cellulose-based film, FUJITAK, FUJI FILM Corporation) was laminated
on the surface of the polyene containing polarizing film via the UV
adhesive applied to the surface of the film. As a result, the
laminated layer including the polyene containing polarizing film
and the substrate was adhered to the protective film. Next, the
laminated layer was irradiated with UV light at 1000 mJ to cure the
UV adhesive. Subsequently, the substrate was separated from the
polyene containing polarizing film.
[0078] Next, the UV adhesive was applied to a thickness of 2 .mu.m
on the backside of the polyene containing polarizing film (a
surface of the polyene containing polarizing film exposed by
separation from the substrate). A 50 .mu.m thick retardation film
(.lamda./4 plate, WRS, Teijin Chemicals Ltd.) was attached to the
backside of the polyene containing polarizing film such that an
angle defined between an optical absorption axis of the polyene
containing polarizing film and a slow axis of the A/4 plate was
45.degree., followed by curing the UV adhesive in the same manner
as above to fabricate a polarizing plate for evaluation.
Comparative Example
[0079] A polyene containing polarizing film and a polarizing plate
according to Comparative Example were fabricated by the following
treatment.
[0080] First, polyvinyl alcohol (JC-25, Japan VAM & POVAL Co.,
Ltd.) was introduced into water as a solvent. The mixture of water
and polyvinyl alcohol was heated while being stirred, thereby
sufficiently dissolving polyvinyl alcohol in water. Leveling agent
(Megapak, DIC Corporation) was added to the aqueous solution of
polyvinyl alcohol, followed by stirring to fabricate a coating
liquid. The ratio (weight ratio) of water, polyvinyl alcohol and
leveling agent in the coating liquid was 90 wt %:10 wt %:0.002 wt
%. Here, the content of the leveling agent was 0.002 wt % based on
the total weight of water and polyvinyl alcohol.
[0081] Next, a non-stretched film formed of isophthalic acid
copolymeric polyethylene terephthalate (PET) was prepared as a
substrate, followed by coating the coating liquid onto the
substrate. Subsequently, the coating liquid was dried to fabricate
a polyvinyl alcohol film. The polyvinyl alcohol film had a
thickness of 10 .mu.m.
[0082] Next, the polyvinyl alcohol film was dipped in an aqueous
solution of 0.5 wt % hydrochloric acid (containing 0.5 wt %
hydrochloric acid based on the total weight of the aqueous
hydrochloric acid solution) adjusted to 10.degree. C., followed by
wet stretching of the polyvinyl alcohol film to 3 times an initial
length thereof in a set or predetermined direction. Namely, in
Comparative Example, the polyvinyl alcohol film was impregnated in
an aqueous hydrochloric acid solution, and then subjected to wet
stretching.
[0083] The polyvinyl alcohol film was removed from the aqueous
hydrochloric acid solution, followed by placing the film in an oven
preheated to 65.degree. C. Thereafter, the polyvinyl alcohol film
was dried at 65.degree. C. for 15 minutes. The resulting polyvinyl
alcohol film was placed in an oven preheated to 130.degree. C.,
followed by dry stretching the film to 2 times the initial length
thereof in the same direction as in wet stretching. Namely, the
polyvinyl alcohol film was stretched to a total length of 6 times
the initial length thereof. Subsequently, the polyvinyl alcohol
film was heated to 130.degree. C. for 30 minutes, followed by
dehydrating the polyvinyl alcohol film to fabricate a polyene
containing polarizing film. Then, a polarizing plate was fabricated
through the same procedure as in Example 1.
[0084] Property Evaluation
[0085] The degree of polarization and transmittance (simple
substance transmittance) of the polarizing plates according to
Example 1 and Comparative Example were evaluated in accordance with
the following treatment.
[0086] Measurement instrument: UV-Vis spectrophotometer (V7100,
fabricated by JASCO Corporation)
[0087] Measurement method: Transmittance (T), parallel
transmittance (Tp), and crossed transmittance (perpendicular
transmittance) (Tc) of the polarizing device were measured. These
represent Y values obtained by measuring 2 degree viewing angle (C
light source) in accordance with JIS Z8701, followed by color
correction. The degree of polarization was calculated from Equation
1 using these transmittance values.
Degree of polarization(P)(%)={(Tp-Tc)/(Tp+Tc)}.sup.1/2.times.100
Equation 1
[0088] Measurement results are shown in Table 1.
TABLE-US-00001 TABLE 1 T P Example 1 44.90% 97.085% Comparative
Example 44.03% 96.506%
[0089] According to this evaluation, it may be observed that the
polarizing plate according to Example 1 exhibits both high degree
of polarization and high transmittance. On the contrary, the
polarizing plate according to Comparative Example exhibits both low
degree of polarization and transmittance. Since the coating liquid
includes an organic acid as an acid catalyst in Example 1, a high
concentration of the acid catalyst is uniformly dispersed in the
polyvinyl alcohol film. Further, since the organic acid has low
volatility, the acid catalyst is unlikely to volatilize in
preparation of polyene. Accordingly, in Example 1, multiple
carbon-carbon double bonds are uniformly formed, thereby providing
a high degree of polarization and high transmittance. On the other
hand, in Comparative Example, since the polyvinyl alcohol film is
impregnated with an aqueous hydrochloric acid solution,
hydrochloric acid is non-uniformly dispersed in polyvinyl alcohol
film. In addition, since hydrochloric acid tends to volatize, the
acid catalyst is vaporized in preparation of polyene. Thus, not
only is the number of carbon-carbon double bonds less than that of
Example 1, but also the distribution of the double bonds is
non-uniform.
Examples 2 to 4
[0090] In Examples 2 to 4, content ratio of paratoluene sulfonic
acid to polyvinyl alcohol was varied. In Examples 2 to 4, a series
of procedures was performed in the same manner as in Example 1
except that the content ratio of paratoluene sulfonic acid and
dehydration time (heating time) upon dry stretching were changed as
listed in Table 2, thereby fabricating dry-stretched films
according to Examples 2 to 4. Each of these dry stretched films
included a polyvinyl alcohol film and a substrate.
[0091] Further, transmittance (single transmittance) of the
dry-stretched films prepared in Examples 2 to 4 was measured in the
same manner as in Example 1. Measurement results are shown in Table
2. Further, the transmittance of the dry-stretched film prepared in
Example 1 is also listed in Table 2.
TABLE-US-00002 TABLE 2 Content of acid Dehydration catalyst Time
Transmittance Example 1 5 wt % 2 min. 40.3% Example 2 10 wt % 1
min. 27% Example 3 4 wt % 10 min. 39% Example 4 2 wt % 45 min.
40%
[0092] Although the transmittance of the polarizing films prepared
in Examples 1, 3 and 4 was less than 44%, the transmittance could
be increased to 44% or more by subjecting the dry stretched film to
wet stretching as in Example 1. In addition, although the
transmittance of the polarizing film prepared in Example 2 was
lower than that of the polarizing films prepared in Examples 1, 3
and 4, the transmittance of the polarizing film of Example 2 could
be increased to about 40% by changing the dehydration time to less
than 1 minute. Namely, since dehydration proceeded rapidly when the
content ratio of the acid catalyst was high, reaction proceeded
excessively only for a dehydration time of 1 minute. Thus, in
Example 2, the transmittance of the polarizing film could be
enhanced to about 40% by reducing the dehydration time. Further, in
Example 4, although the transmittance of the polarizing time was
high, dehydration was performed for too long a time. When
polarizing films are produced in a roll-to-roll manner, drying time
increases with increasing dehydration time. As such, the content of
the acid catalyst may be from 4 wt % to 10 wt % in terms of having
good transmittance and dehydration time.
[0093] The method of fabricating a polyene containing polarizing
film according to this embodiment includes fabricating a polyvinyl
alcohol film using a coating liquid including an acid catalyst and
a polyvinyl alcohol, and dehydrating the polyvinyl alcohol
film.
[0094] The method allows a high concentration of the acid catalyst
to be uniformly dispersed in the polyvinyl alcohol film, thereby
enabling fabrication of a polyene containing polarizing film in
which multiple carbon-carbon double bonds are uniformly formed
without the need of accurate control of temperature and the like as
in the related art. Therefore, the method according to the
embodiment of the invention is capable of stably fabricating a
polyene containing polarizing film having both high degree of
polarization and high transmittance, i.e., a polarizing film having
excellent optical properties.
[0095] In addition, the polyene containing polarizing film having
high degree of polarization and high transmittance is suitable for
anti-reflective polarizing plates for organic light emitting
displays, which are expected to have widespread use in the near
future. Since the polyene containing polarizing film has (e.g.,
essentially has) strong durability with respect to high temperature
and high humidity, the polyene containing polarizing film according
to the embodiment of the invention exhibits not only excellent
optical properties but also high durability with respect to high
temperature and high humidity. A display device including such a
polyene containing polarizing film may have improved optical
properties.
[0096] Further, since the acid catalyst is low volatile, the acid
catalyst is unlikely to evaporate in preparation of polyene.
Accordingly, the method according to the embodiment of the
invention may provide a more uniform acid concentration in
polyvinyl alcohol even during preparation of polyene.
[0097] Further, since the acid catalyst has a weight loss rate of
less than 3 wt % at 100.degree. C., the acid catalyst is unlikely
to evaporate in preparation of polyene. Accordingly, the method
according to the embodiment of the invention may provide a more
uniform acid concentration in polyvinyl alcohol in preparation of
polyene.
[0098] Further, since the acid catalyst is an organic acid, the
acid catalyst is unlikely to evaporate in preparation of polyene.
Accordingly, the method according to the embodiment of the
invention may provide a more uniform acid concentration in
polyvinyl alcohol in preparation of polyene.
[0099] Further, since the organic acid has a functional group
selected from the group consisting of a carboxylic acid group and a
sulfonic acid group, the organic acid is unlikely to evaporate in
preparation of polyene. Accordingly, the method according to the
embodiment of the invention may provide a more uniform acid
concentration in polyvinyl alcohol in preparation of polyene.
[0100] Furthermore, in the method according to the embodiment of
the invention, the coating liquid includes the acid catalyst in an
amount of 2 wt % to 10 wt %, for example, in an amount of 4.0 wt %
to 10.0 wt %, based on the weight of the polyvinyl alcohol.
Therefore, the method according to the embodiment of the invention
may provide a polyene containing polarizing film having both high
degree of polarization and high transmittance.
[0101] The content of the acid catalyst may be 5 wt % based on the
weight of polyvinyl alcohol, and hence the method according to the
embodiment of the invention may provide a polyene containing
polarizing film having both a high degree of polarization and high
transmittance.
[0102] Furthermore, the method according to the embodiment of the
invention may reduce the thickness of the polyene containing
polarizing film. For example, the method according to the
embodiment of the invention may reduce the thickness of the polyene
containing polarizing film to less than 10 .mu.m. As a result,
shrinkage of the polyene containing polarizing film and bending of
a large organic light emitting display may be suppressed even when
the polyene containing polarizing film is applied to a large
organic light emitting display.
[0103] Although some embodiments have been provided with reference
to the accompanying drawings, it should be understood that these
embodiments are given by way of illustration only, and that various
modifications, variations, and alterations may be made without
departing from the spirit and scope of the present invention. The
scope of the present invention should be limited only by the
accompanying claims and equivalents thereof.
* * * * *